High-molecular-weight polyazoles

ABSTRACT

The invention under consideration concerns novel high-molecular-weight polyazoles, which are suitable for the production of fibers, films, membranes, and molded articles, on the basis of their high molecular weight, expressed as intrinsic viscosity, of at least 1.3 dl/g. Moreover, the invention under consideration describes a method for the production of high-molecular-weight polyazoles.

The invention under consideration concerns novel high-molecular-weightpolyazoles, a method for their production, and their use.

Polyazoles, such as polybenzimidazoles (^(R)Celazole), have been knownfor a long time. The production of such polybenzimidazoles (PBI) usuallytakes place by reacting 3,3′,4,4′-tetra-aminobiphenyl with isophthalicacid or diphenyl isophthalate or their esters in the melt. In thereaction with DPIP, gaseous phenol is formed as a secondary product,which leads to a strong formation of foam and volume expansion. Theformed prepolymer solidifies in the reactor and is subsequentlycomminuted mechanically. The powdery prepolymer is then end-polymerizedin a solid phase polymerization at temperatures of up to 400° C., andthe desired polybenzimidazoles are obtained.

For the production of polymer films or polymer fibers, the PBI isdissolved in another step in polar, aprotic solvents, such as dimethylacetamide (DMAc), and a film or a fiber is produced by means ofclassical methods.

In the production of the solutions, it has been shown that they dependgreatly on the characteristics of the polyazole used. In particular, theobserved gel formations and other crystallization effects lead to a lowstorage capacity of the solutions. These problems have already beendescribed in German Patent Application No. 10052237.8. The proceduredescribed there, however, is very expensive and leads to a poor yield ofthe polyazole polymers used.

The goal of the invention under consideration is to prepare a polyazole,which overcomes the preceding problems and, on the other hand, exhibitsexcellent physical characteristics.

It was then discovered that high-molecular-weight polyazoles, on the onehand, lead to the formation of storage-stable solutions and, on theother hand, even surpass the excellent physical characteristics ofpreviously known polyazoles. The high-molecular-weight polyazoles are,moreover, prepared in a simple manner.

The objective of the invention under consideration refers to polyazoleswhose molecular weights, measured as intrinsic viscosity, is at least1.3 dl/g, obtainable by a method consisting of the following steps:

A) mixing one or more aromatic tetra-amino compounds with one or morearomatic carboxylic acids or its esters, which contain at least two acidgroups per carboxylic acid monomer, or mixing one or more aromaticand/or heteroaromatic diaminocarboxylic acids;

B) heating the mixture obtainable according to step B) under inert gas,to temperatures of up to 350° C., preferably up to 300° C.;

C) comminution of the composition obtained according to step B) andfractionation of the particles obtained;

D) heating the particle fraction of 300 μm to 1000 μm under an inertgas, to temperatures of up to 450° C., preferably up to 400° C., andcooling.

The aromatic and heteroaromatic tetra-amino compounds, used inaccordance with the invention, are preferably3,3′,4,4′-tetra-aminobiphenyl, 2,3,5,6-tetra-aminopyridine,1,2,4,5-tetra-aminobenzene, 3,3′,4,4′-tetra-aminodiphenylsulfone,3,3′,4,4′-tetra-aminodiphenyl ether, 3,3′,4,4′-tetra-aminobenzophenone,3,3′,4,4′-tetra-aminodiphenyl methane, and3,3′,4,4′-tetra-aminodiphenyldimethylmethane,

and their salts, in particular, their mono-, di-, tri-, andtetrahydrochloride derivatives.

The aromatic carboxylic acids used, in accordance with the invention,are dicarboxylic acids or its esters, or its anhydrides or its acidchlorides. The term “aromatic carboxylic acids” equally comprisesheteroaromatic carboxylic acids as well. Preferably, the aromaticdicarboxylic acids are isophthalic acid, terephthalic acid, phthalicacid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid,2-hydroxyterephthalic acid, 5-aminoisophthalic acid,5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic acid,2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid,4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid,2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 3-fluorophthalicacid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid,tetrafluorophthalic acid, tetrafluoroisophthalic acid,tetrafluoroterephthalic acid, 1,4-naphthalenedicarboxylic acid,1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,2,7-napthalenedicarboxylic acid, diphenic acid,1,8-dihydroxynaphthalene-3,6-dicarboyxlic acid, diphenylether-4,4′-dicarboxylic acid, benzophenone-4,4′-dicarboxylic acid,diphenylsulfone-4,4′-dicarboyxlic acid, biphenyl-4,4′-dicarboxylic acid,4-trifluoromethylphthalic acid,2,2-bis(4-arboxyphenyl)hexafluoropropane, 4,4′-stilbenedicarboxylicacid, 4-carboxycinnamic acid, or their C1-C20-alkyl estersor C5-C12-arylesters, or their acid anhydrides or their acid chlorides.

The heteroaromatic carboxylic acids used, in accordance with theinvention, are heteroaromatic dicarboxylic acids or their esters ortheir anhydrides. The “heteroaromatic dicarboxylic acids” includearomatic systems that contain at least one nitrogen, oxygen, sulfur, orphosphorus atom in the ring. Preferably, it is pyridine-2,5-dicarboxylicacid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid,pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridine dicarboxylic acid,3,5-pyrazole dicarboxylic acid, 2,6-pyrimidine dicarboxylic acid,2,5-pyrazine dicarboxylic acid, 2,4,6-pyridine tricarboxylic acid, andbenzimidazole-5,6-dicarboxylic acid, as well as their C1-C20-alkylesters or C5-C12-aryl esters, or their acid anhydrides or their acidchlorides.

The aromatic and heteroaromatic diaminocarboxylic acid used inaccordance with the invention is preferably diaminobenzoic acid and itsmono- and dihydrochloride derivatives.

Preferably, mixtures of at least 2 different aromatic carboxylic acidsare used in step A). With particular preference, mixtures that, inaddition to aromatic carboxylic acids, also contain heteroaromaticcarboxylic acids are used. The mixture ratio of aromatic carboxylicacids to heteroaromatic carboxylic acids is between 1:99 and 99:1,preferably, 1:50 to 50:1.

These mixtures are, in particular, mixtures of N-heteroaromaticdicarboxylic acids and aromatic dicarboxylic acids or their esters.Non-limiting examples are isophthalic acid, terephthalic acid, phthalicacid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid,4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid,2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid,1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,diphenic acid, 1,8-dihydroxynapthalene-3,6-dicarboxylic acid, diphenylether-4,4′-dicarboxylic acid, benzophenone-4,4′-dicarboxylic acid,diphenylsulfone-4,4′-dicarboxylic acid, biphenyl-4,4′-dicarboxylic acid,4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid,pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid,pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid,3,5-pyrazoledicarboxylic acid, 2,6-pyrimidine dicarboxylic acid, and2,5-pyrazine dicarboxylic acid. Preferably, it is diphenyl isophthalate(DPIP) and its ester.

The polymers formed in accordance with the invention, on the basis ofpolyazole, contains recurring azole units of general formula (I) and/or(II) and/or (III) and/or (IV) and/or (V) and/or (VI) and/or (VII) and/or(VIII) and/or (DC) and/or (X):

wherein

-   Ar are the same or different and [stand] for a tetravalent,    aromatic, or heteroaromatic group, which can be mononuclear or    multinuclear;-   Ar¹ are the same or different and [stand] for a divalent aromatic or    heteroaromatic group, which can be mononuclear or multinuclear;-   Ar² are the same or different and [stand] for a divalent or    trivalent aromatic or heteroaromatic group, which can be mononuclear    or multinuclear;-   Ar³ are the same or different and [stand] for a trivalent aromatic    or heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁴ are the same or different and [stand] for a trivalent aromatic    or heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁵ are the same or different and [stand] for a tetravalent aromatic    or heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁶ are the same or different and [stand] for a divalent aromatic or    heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁷ are the same or different and [stand] for a divalent aromatic or    heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁸ are the same or different and [stand] for a trivalent aromatic    or heteroaromatic group, which can be mononuclear or multinuclear;-   Ar⁹ are the same or different and [stand] for a divalent or    trivalent aromatic or heteroaromatic group, which can be mononuclear    or multinuclear;-   Ar¹⁰ are the same or different and [stand] for a divalent or    trivalent aromatic or heteroaromatic group, which can be mononuclear    or multinuclear;-   Ar¹¹ are the same or different and [stand] for a divalent aromatic    or heteroaromatic group, which can be mononuclear or multinuclear;-   X is the same or different and [stands] for oxygen, sulfur, or an    amino group, which carries a hydrogen atom, a group with 1-20 carbon    atoms, preferably, a branched or nonbranched alkyl or alkoxy group,    or an aryl group as an additional radical;    n is a whole number greater than [or] equal to 10, preferably    greater than [or] equal to 100.

Preferred aromatic or heteroaromatic groups are derived from benzene,naphthalene, biphenyl, diphenyl ether, diphenylmethane,diphenyldimethylmethane, bisphenone, diphenyl sulfone, quinoline,pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine,tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole, benzotriazole,benzo-oxathiadiazole, benzo-oxadiazole, benzopyridine, benzopyrazine,benzopyrazidine, benzopyrnmidine, benzopyrazine [sic], benzotriazine,indolizine, quinolizine, pyridopyridine, imidazopyrimidine,pyrazinopyrimidine, carbazole, acridine, phenazine, benzoquinoline,phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline,and phenanthrene, which, if necessary, can also be substituted.

The substitution pattern of Ar¹, Ar⁴, Ar⁶, Ar⁷, Ar⁸, Ar⁹, Ar¹⁰, and Ar¹¹is thereby arbitrary; in the case of phenylene, for example, Ar¹, Ar⁴,Ar⁶, Ar⁷, Ar⁸, Ar⁹, Ar¹⁰, and Ar¹¹ can be ortho-, meta-, andpara-phenylene. Particularly preferred groups are derived from benzeneand biphenylene, which can, under certain circumstances, also besubstituted.

Preferred alkyl groups are short-chain alkyl groups with 1 to 4 carbonatoms, such as methyl, ethyl, n- or i-propyl, and t-butyl groups.

Preferred aromatic groups are phenyl or naphthyl groups. The alkylgroups and the aromatic groups can be substituted.

Preferred substituents are halogen atoms such as fluorine, amino groups,hydroxy groups, or short-chain alkyl groups such as methyl or ethylgroups.

Preferred are polyazoles with recurring units of formula (I), in whichthe radicals X are the same within a recurring unit.

The polyazoles can basically also have different recurring units thatdiffer, for example, in their radical X. Preferably, however, they onlyhave the same radicals X in a recurring unit.

Other preferred polyazole polymers are polyimidazoles,polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines,polythiadiazoles poly(pyridines), poyl(pyrimidines), andpoly(tetrazapyrenes).

In another embodiment of the invention under consideration, the polymercontaining recurring azole units is a copolymer or a blend that containsat least two units of formulas (I) to (X), which differ from oneanother. The polymers can be present as block copolymers (diblock,triblock), random copolymers, periodic [sic] copolymers, and/oralternating polymers.

In a particularly preferred embodiment of the invention underconsideration, the polymer containing recurring azole units is apolyazole that contains only units of formula (I) and/or (II).

The number of the recurring azole units in the polymer is preferably awhole number greater than [or] equal to 10. Particularly preferredpolymers contain at least 100 recurring azole units.

Within the framework of the invention under consideration, polymerscontaining recurring benzimidazole units are preferred. Some examples ofthe extremely appropriate polymers containing recurring benzimidazoleunits are expressed by the following formulas:

wherein n and m is a whole number greater than [or] equal to 10,preferably greater than [or] equal to 100.

The polyazoles in accordance with the invention, in particular thepolyenzimidazoles, are characterized by a high molecular weight.Measured as intrinsic viscosity, it is at least 1.3 dl/g, in particularat least 1.4 dl/g, and thus is clearly above that of commercialpolybenzimidazole (IV<1.1 dl/g).

The heating according to step B) takes place under an inert gas,preferably with the exclusion of moisture. The heating takes place for aperiod of 30 minutes to 24 hours, preferably between 1 hour and 15hours, and in particular between 2 hours and 10 hours. For a betterdistribution of the heat to be introduced, it is advantageous to providefor a thorough mixing of the mass to be heated. Preferably, the mass isstirred in step B). This has an additional advantage, since the foamformation observed in the temperature range of 170 to 270° C. can becontrolled or reduced. It is advantageous to select a stirrer that issuitable for bringing about, in step C), the comminution of thefoam-like mass obtained in accordance with step B). The particlesobtained can be comminuted further if the comminution with the availablestirrer was still insufficient.

To determine the particle size and the particle size distribution, anumber of measuring methods exist. Within the framework of thisinvention, screen analysis is sufficient for the particle sizedetermination, so that a fractionation by screening takes place in stepC).

Basically, however, all other fractionating methods that lead to acorresponding division [separation] are also suitable.

For the fractionation, in accordance with the invention, a set ofscreens with different mesh widths are arranged one over the other in ascreening machine. In the screen analysis, the particle size isdetermined by the mesh width of that screen which barely allows theparticle (screen passage, undersize material) to pass. The screens arerepresented in units of micrometers according to the inside mesh width.

In this way, the particle fraction of 300 μm to 1000 μm is separatedfrom the remaining particles, and is subsequently used in step D). Thematerials used in step D) contain at least 90 wt % of the particlefraction of 300 μm to 1000 μm, preferably at least 95 wt %, and inparticular at least 98 wt %.

The fractionation of the particles in step C) preferably takes placeunder an inert gas and with the exclusion of moisture. Should this notbe possible, then a drying of the particle fraction to be processedfurther may be required. The residual water content of the particlesused in step D) should not exceed 5 wt %, preferably 3 wt %, and inparticular 1 wt %. The drying can take place by means of known methods.

Subsequently, in step D) the particle fraction of 300 μm to 100 μm isheated under an inert gas, preferably, with the exclusion of moisture,to temperatures of up to 450° C., preferably up to 400° C. The minimumtemperature in step [D)] is 300° C., preferably more than 350° C. As afunction of the selected temperature, the treatment time is between 15minutes and up to 24 hours, preferably between 30 minutes and 15 hours,and in particular between 1 hour and 10 hours. To better distribute theheat to be brought in, it is advantageous to provide for a thoroughmixing of the mass to be heated. Preferably, stirring is carried out instep D).

In another embodiment of the invention, step D) can be carried out in aseparate reactor, and the desired partial fraction can be placed inintermediate storage as a depot substance. Preferably, step D) iscarried out in a separate reactor.

In step D), the condensation to the polyazole polymer and the buildup ofthe high molecular weight take place.

After cooling, the molecular weight can be determined.

The polyazoles in accordance with the invention, in particular thepolybenzimidazoles, are characterized by a high molecular weight.Measured as intrinsic viscosity, it is at least 1.3 dl/g, in particularat least, 1.4 dl/g, and is thus clearly above that of commercialpolybenzimidazole (IV<1.1 dl/g).

As a result of the high molecular weight, the polyazoles, in accordancewith the invention, are particularly good for the production of moldedarticles, fibers, in particular, high-strength fibers, and films inwhich high demands are made on the mechanical characteristics. Anotheradvantage of the high-molecular-weight polyazole, in accordance with theinvention, is to be found in the fact that it forms more stablesolutions, which have an improved storage capacity.

Thus, the objective of the invention under consideration also refers tosolutions of the high-molecular-weight polyazole, in accordance with theinvention, in polar, aprotic solvents, particularly in dimethylacetamide. The general production of such solutions is, for example,described in German Patent Application No. 10,052,237.8. Such solutionsare suitable for the coating of surfaces, in particular metal surfaces.

Another objective of the invention under consideration refers to moldedarticles obtained by sintering or tempering the high-molecular-weightpolyazole, in accordance with the invention, preferably by sintering ortempering in molds.

It has hereby proved advantageous if the high-molecular-weightpolyazole, in accordance with the invention, exhibits a crosslinking.If, the material in accordance with this invention is used in this way,tricarboxylic acids or tetracarboxylic acids are also added in step A).In this way, the desired branching/crosslinking in the polymer, inaccordance with the invention, is attained.

The tricarboxylic acids and tetracarboxylic acids or their esters, ortheir anhydrides or their acid chlorides, added in step A), arepreferably their C1-C20-alkyl esters or C5-C12-aryl esters. Particularlypreferred is 1,3,5-benzene-tricarboxylic acid (trimesic acid),1,2-4-benzene-tricarboxylic acid (trimellitic acid),(2-carboxyphenyl)iminodiacetic acid, 3,5,3′-biphenyl tricarboxylic acid,3,5,4′-biphenyl tricarboxylic acid, 3,5,3′,5′-biphenyl tetracarboxylicacid, 1,2,4,5-benzene-tetracarboxylic acid, benzophenotetracarboxylicacid, 3,3′,4,4′-biphenyl tetracarboxylic acid, 2,2′,3,3′-biphenyltetracarboxylic acid, 1,2,5,6-naphthalene-tetracarboxylic acid, or1,4,5,8-naphthalene-tetracarboxylic acid.

The content of tricarboxylic acid or tetracarboxylic acids (relative tothe used dicarboxylic acid) is between 0 and 30 mol %, preferablybetween 0.1 and 20 mol %, and in particular between 0.5 and 10 mol %.

Also, such high-molecular-weight polyazoles are the objective of theinvention under consideration.

The films produced from the high-molecular-weight polyazole solutions,in accordance with the invention, exhibit improved materialcharacteristics in comparison with the previously known polymer filmsand are suitable as separation membranes.

Such separation membranes can be produced as dense polymer films, poroushollow fiber membranes, or as porous, open-cell polymer films,optionally with a compact cover layer.

For the production of a porous membrane, a polymer solution, inaccordance with the invention, can also contain a so-called pore-formingagent such as glycerol, which, depending on the selection of thecomposition of the precipitating agent, lead to different morphologiesof the separation membranes.

For separation purposes, the following structures are preferred: i)symmetrical, porous structure; ii) asymmetrical porous structure with apolymer compression close to a membrane surface.

Scanning electron micrographs of such particularly suitable structuresof polybenzimidazole membranes are disclosed in Journal of MembraneScience, Volume 20, 1984, pages 147-66.

Such phase inversion membranes and structures are known to the expert.Membranes with a symmetrical porous structure are used as separation andfiltration membranes for air and gas filtration, or for micro- orultrafiltration for liquids. Membranes with an asymmetrical, porousstructure can be used in many diverse ways for reverse osmosis, inparticular, water desalination, dialysis, or the preparation of gases.

A particularly appropriate use is the separation of hydrogen and carbondioxide from gas mixtures in combination with a porous metal carrier.Alternative technologies for the CO₂ separation require a cooling of thegases to 150° C. because of the low thermal stability of the polymermembrane, wherein the efficiency is reduced. The separation membranesbased on polyazoles, in accordance with the invention, can be operatedcontinuously up to a temperature of 400° C. and thus lead to an increasein yield and a reduction of costs.

For additional information on separation membranes based on polyazoles,reference is made to the technical literature, in particular to thefollowing patents: World Patent No. 98/14505; U.S. Pat. Nos.A-4,693,815; A-4,693,824; A-375,262; A-3,737,042; A-4,512,894;A-448,687; A-3,841,492. The disclosure regarding the structure and theproduction of separation membranes, contained in the literaturereferences previously mentioned, is included by the invention underconsideration and is a component of the description under consideration.In particular, such separation membranes can be produced in the form offlat films or as hollow fiber membranes.

To further improve the application-technical characteristics, fillers,in particular, nano-scale fillers, can be added to the polymer film.

Nonlimiting examples of such fillers are the following:

-   oxides: such as Al₂O₃, Sb₂O₅, ThO₂, SnO₂, ZrO₂, MoO₃-   silicates: such as zeolites, zeolite(NH₄+), layered silicates,    skeletal silicates, N-natrolites,-   H-mordenites, NH₄-analcines, NH₄-sodalites, NH₄-gallates,    H-montmorillonites-   fillers: such as carbides, in particular SiC, Si₃N₄, fibers, in    particular, glass fibers, glass powders, and/or polymer fibers,    preferably based on polyazoles.

As additional components, the polymer film can also contain additivesthat trap or destroy the radicals that may be produced, in operation,during the gas filtration.

Nonlimiting examples of such additives are the following:

bis(trifluoromethyl)nitroxide, 2,2-diphenyl-1-picrinylhydrazyl, phenols,alkyl phenols, sterically hindered alkyl phenols such as Irganox,aromatic amines, sterically hindered amines such as Chimassorb;sterically hindered hydroxyl amines, sterically hindered alkyl amines,sterically hindered hydroxyl amines, sterically hindered hydroxylamineethers, phosphites such as Irgafos, nitrosobenzene,methyl-2-nitrosopropane, benzophenone, benzaldehyde-tert-butylnitron,cysteamine, melanines, lead oxides, manganese oxides, nickel oxides, andcobalt oxides.

Among the possible fields of application of the polymer films, inaccordance with the invention, are, among others, the use as a filtermedium in gas filtration and separation or gas purification, and inreverse osmosis, as substrates for flexible electrical wiring, asbattery separators, as protective films for electrical cables, asinsulators in electrical components and apparatuses, such as condensers,and as protective films for metal and other surfaces.

The fibers produced from the high-molecular-weight polyazole solutions,in accordance with the invention, exhibit improved materialcharacteristics, such as strength and elastic modulus, in comparisonwith the previously known polymer fibers, and are suitable, inparticular, for the production of high-tenacity fibers. If the fibersare to be used for textiles, they are also treated with dilute sulfuricacid at a temperature above 400° C., preferably above 450° C. Thehigh-tenacity fibers are used as reinforcement fibers in so-calledcomposite materials, compound materials, and fiber-reinforced moldedarticles, also based on the polymer.

Another objective of the invention under consideration thus refers topolymer fibers based on polyazoles whose molecular weights, expressed asintrinsic viscosity, are 1.3 dl/g, preferably at least 1.4 dl/g.

The production of these fibers takes place by means of known methods.Within the framework of the invention under consideration, a solution ofthe high-molecular-weight polyazole in accordance with the invention, inpolar, aprotic solvents, particularly in dimethyl acetamide, is extrudedby means of the methods known for PBI; subsequently, the solvent isremoved with known methods.

The formed fibers can be continuous filaments or—if the fiber formationtakes place analogous to the “melt blow method”—can have a staple fibercharacter. The titer of the formed fibers has no limitation, so thatmonofilaments, that is, wire-type fibers, can be produced. In addition,hollow fibers can also be produced. The desired titer is determined bythe intended use of the fibers. The entire handling of the formed fiberscan take place by means of known fiber technologies (see CompleteTextile Glossary, Celanese Acetate LLC, 2000).

In one variant, the freshly formed, still solvent-containing fibers canbe introduced into a precipitation bath. This introduction is done inthe temperature range between room temperature (20° C.) and the boilingtemperature of the precipitation liquid (under standard pressure).

As a precipitation liquid in the sense of the invention, solventspresent as liquids at room temperature (that is, 20° C.)—selected fromthe group of alcohols, ketones, alkanes (aliphatic and cycloaliphatic),ethers (aliphatic and cycloaliphatic), esters, carboxylic acids, whereinthe preceding [sic] group members can be halogenated, water, inorganicacids (such as H₃PO₄, H₂SO₄), and mixtures of the same—are used.

Preferably, C1-C10 alcohols, C2-C5 ketones, C1-C10-alkanes (aliphaticand cycloaliphatic), C2-C6-ethers (aliphatic and cycloaliphatic), C2-C5esters, C1-C3 carboxylic acids, dichloromethane, water, and mixtures ofthe same are used.

Subsequently, the fiber is freed from the precipitation liquid. This ispreferably done by drying, wherein the temperature and the ambientpressure are selected as a function of the partial vapor pressure of theprecipitation liquid. Usually, the drying is done under standardpressure and at temperatures between 20° C. and 200° C. Also, moregentle drying can be carried out under vacuum. The drying method is notsubject to any limitations.

The treatment in the precipitation bath can lead to the formation ofporous structures, in particular, with hollow fibers. Depending on theuse, these are desired for subsequent use.

As already stated before, the films produced from thehigh-molecular-weight polyazole solutions, in accordance with theinvention, have improved material characteristics, in comparison withthe previously known polymer films, and are excellent as startingmaterials for the production of proton-conducting membranes.

For the production of proton-conducting membranes, a film is first castfrom the polymer solution, in accordance with the invention, and thesolvent is removed. To this end, the measures described in German PatentApplication No. 10109829.4 are preferably carried out. Subsequently, thehigh-molecular-weight polymer film is wetted with a doping agent andplaced in it. As doping agents for the polymer membranes, in accordancewith the invention, acids, preferably all known Lewis and Bronstedacids, in particular inorganic Lewis and Bronsted acids, or alkalihydroxides, are used. In addition to this previously mentioned acid, theuse of polyacids is also possible, in particular isopolyacids andheteropolyacids, and mixtures of various acids. In the sense of theinvention under consideration, heteropolyacids designate inorganicpolyacids with at least two different central atoms, which are formedfrom weak, multibasic oxygen acids of a metal (preferably, Cr, Mo, V, W)and a nonmetal (preferably, As, I, P, Se, Si, Te) as partial, mixedanhydrides. Those belonging in this group are, among others,12-molybdatophosphoric acid and 12-tungstophosphoric acid.

Doping agents that are particularly preferred in accordance with theinvention are sulfuric acid, phosphoric acid, and potassium hydroxide. Avery particularly preferred doping agent is phosphoric acid (H₃PO₄).

The polymer membranes, in accordance with the invention, are doped.Within the framework of the invention under consideration, doped polymermembranes designate those polymer membranes that exhibit an increasedproton conducting capacity, in comparison with the nondoped polymermembranes, as a result of the presence of doping agents.

Method for the production of doped polymer membranes are known. In apreferred embodiment of the invention under consideration, they areobtained by wetting a film of the pertinent polymer with concentratedacid, preferably with highly concentrated phosphoric acid, over asuitable time, preferably 5 minutes to 96 hours, with particularpreference 1-72 hours, at temperatures between room temperature and 100°C. and, optionally, under increased pressure.

The conducting capacity of the polymer membranes, in accordance with theinvention, is affected by the degree of doping. The conducting capacityincreases with an increasing concentration of doping agents, until amaximum value is attained. In accordance with the invention, the degreeof doping is indicated as moles of acid per mole of repetition units ofthe polymer. Within the framework of the invention under consideration,a degree of doping between 3 and 15, in particular between 6 and 12, ispreferred.

The polymer membrane, in accordance with the invention, has improvedmaterial characteristics in comparison with the previously known, dopedpolymer membranes. In particular, they have very good mechanicalcharacteristics and, in comparison with conventional membranes, theyexhibit an improved service life.

The possible application areas of the doped polymer membranes, inaccordance with the invention, are, among others, the use in fuel cells,in electrolysis, in condensers, and in battery systems. As a result oftheir characteristics profile, the doped polymer membranes arepreferably used in fuel cells.

The invention under consideration also refers to a membrane-electrodeunit, which has at least a polymer membrane, in accordance with theinvention. For more information regarding membrane-electrode units,reference is made to the technical literature, in particular, thefollowing patents: U.S. Pat. Nos. A-4,191,618; A-4,212,714; andA-4,333,805. The disclosure contained in the references mentioned in thepreceding (U.S. Pat. Nos. A-4,191,618; A-4,212,714; and A-4,333,805),with regard to the structure and the production of membrane-electrodeunits, is also a component of the description [of the invention].

For the determination of the intrinsic viscosity (IV), the polymer isfirst dried at 160° C. for 2 hours. 100 mg of the polymer thus dried arethen dissolved in 100 mL of concentrated sulfuric acid (at least 96 wt%) at 80° C., for 4 hours. The intrinsic viscosity is determined fromthis solution, in accordance with ISO 3105, with an Ubbelhodeviscosimeter, at a temperature of 25° C.

EXAMPLES Example 1

214.27 g of TAB (tetra-aminobiphenyl) and 166.14 g of isophthalic acidwere added, under an N₂ atmosphere, to a quartz reactor equipped with astirrer. Subsequently, the mixture was heated to 150° C., whilestirring, for 1 hour; to 190° C., for 1 hour; to 250° C., for 1 hour;and then to 290° C., for 1.5 hours.

A strong foam formation was observed between 190° C. and 250° C.Subsequently, the formed foam was comminuted into small particles bymeans of the stirrer. After another 1.5 hours, at 290° C., the reactorwas cooled, then the polymer was screened into 5 fractions (<212,212-300, 300-500, 500-1000, and >1000 μm) with a screening machine.

Table I shows the intrinsic viscosities (IV) and portions of theindividual fractions. Subsequently, each individual fraction was pouredinto a quartz reactor and polymerized under a N₂ atmosphere, at 380° C.,while stirring for 3 hours, then cooled, and the IV of the polymer wasmeasured.

The IV results found for the individual polymerization are given inTable I.

TABLE I IV before IV after completion of Particle size [μm] Percent [%]fractionation polymerization  <212 31.16 0.23 0.56 212-300 16.47 0.251.04 300-500 18.94 0.25 1.40  500-1000 27.38 0.26 1.44 >1000 6.06 0.251.17

1. A method of making a polymer based on polyazoles whose molecularweight, measured as intrinsic viscosity in a concentrated (at least 96wt%) sulfuric acid at 25° C., is at least 1.3 dl/g*, comprising thesteps of: A) mixing of one or more aromatic tetra-amino compounds withone or more aromatic carboxylic acids or their esters, which contain atleast two acid groups per carboxylic acid monomers, or mixtures of oneor more aromatic and/or heteroaromatic diaminocarboxylic acids; B)heating of the mixture, which can be obtained according to step B),under an inert gas, to temperatures of up to 350° C., and producing amass; C) comminution of the mass obtained according to step B) andfractionation of the particles obtained; D) heating of the particlefraction of 300 μm to 1000 μm under an inert gas, to temperatures of upto 450° C. ; and cooling.
 2. The method according to claim 1, whereinthe aromatic tetra-amino compounds being selected from the groupconsisting of: 3,3′,4,4′-tetra-aminobiphenyl,2,3,5,6-tetra-aminopyridine, 1,2,4,5-tetra-aminobenzene,3,3′,4′,4′-tetra-aminodiphenylsulfone,3,3′,4,4′-tetra-ammodiphenylether, 3,3′,4,4′-tetra-aminobenzophenone,3,3′,4,4′-tetra-aminodiphenylmethane, and3,3′,4,4′tetra-aminodiphenyldimethymethane, and their salts, and theirmono-, di-, tri-, and tetrahydrochloride derivatives.
 3. The methodaccording to claim 1, wherein the aromatic dicarboxylic acids beingselected from the group consisting of: isophthalic acid, terephthalicacid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalicacid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid,5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic acid,2,5-dihydroxyterephthalic acid, 2,5-dihydroxyisophthalic acid,2,3-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid,2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 3-fluorophthalicacid, 5 fluoroisophthalic acid, 2 fluoroterephthalic acid,tetrafluorophthalic acid, tetrafluoroisophthalic acid,tetrafluoroterephthalic acid, 1,4-naphthalenedicarboxylic acid,1,5-naphthalenedicarboxylic acid, 2,6-napthalenedicarboxylic acid,2,7-naphthalenedicarboxylic acid, diphenic acid,1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenylether4,4′-dicarboxylic acid, benzophenone-4,4′-dicarboxylic acid,diphenylsulfone-4,4′-dicarboxylic acid, biphenyl-4,4′-dicarboxylic acid,4-trifluoromethylphthalic acid, 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4′-stilbenedicarboxylic acid, 4-carboxycinnamicacid, or their C1-C20-alkyl esters or C5-C12-aryl esters, or their acidanhydrides, or their acid chlorides.
 4. The method according to claim 1wherein the aromatic carboxylic acids being selected from the groupconsisting of: tricarboxylic acids, tetracarboxylic acids, or theirC1-20-alkyl esters or C5-C12-aryl esters or their acid anhydrides ortheir acid chlorides.
 5. The method according to claim 1, wherein thearomatic carboxylic acids being selected from the group consisting of:tetracarboxylic acids, their C1-20alkyl esters or C5-C12-aryl esters ortheir acid anhydrides or their acid chlorides.
 6. The method accordingto claim 4, wherein the content of tricarboxylic acids ortetracarboxylic acids (relative to the dicarboxylic acid used) isbetween 0 and 30 mol %.
 7. The method according to claim 1, wherein theheteroaromatic carboxylic acids being selected from the group consistingof: heteroaromatic dicarboxylic acids and tricarboxylic acids andtetracarboxylic acids, which contain at least one nitrogen, oxygen,sulfur, or phosphorous atom in the ring, and their C1-20-alkyl esters orC5-C12-aryl esters, or their acid anhydrides or their acid chlorides. 8.The method according to claim 1, wherein the polymer contains recurringazole units of general formula (I) and/or (II) and/or (III) and/or (IV)and/or (V) and/or (VI) and/or (VII) and/or (VIII) and/or (IX) and/or(X),

wherein, Ar are the same or different and refers to a tetravalent,aromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar¹ are the same or different and refers to a divalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar² are the same or different and refers to a divalent ortrivalent aromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar³ are the same or different and refers to a trivalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁴ are the same or different and refers to a trivalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁵ are the same or different and refers to a tetravalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁶ are the same or different and refers to a divalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁷ are the same or different and refers to a divalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁸ are the same or different and refers to a trivalentaromatic or heteroaromatic group, which can be mononuclear ormultinuclear; Ar⁹ are the same or different and refers to a divalent ortrivalent or tetravalent aromatic or heteroaromatic group, which can bemononuclear or multinuclear; Ar¹⁰ are the same or different and refersto a divalent or trivalent aromatic or heteroaromatic group, which canbe mononuclear or multinuclear; Ar¹¹ are the same or different andrefers to a divalent aromatic or heteroaromatic group, which can bemononuclear or multinuclear; X is the same or different and refers tooxygen, sulfur, or an amino group, which carries a hydrogen atom, agroup with 1-20 carbon atoms, or an aryl group, as an additionalradical; and n is a whole number greater than or equal to 10, preferablygreater than or equal to
 100. 9. The method according to claim 8,wherein the polymer being selected from the group consisting of:polybenzimidazole, poly(pyridines), poly(pyrimidines), polyimidazoles,polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines,polythiadiazoles, and poly(tetrazapyrenes).
 10. The method according toclaim 1, wherein the polymer being a polymer containing recurringbenzimidazole units with the following formula:

wherein n and m are whole numbers greater than or equal to 10,preferably greater than or to
 100. 11. The method according to claim 1,wherein the particle fraction used in step D) contains at least 90 wt %of the particle fraction of 300 μm to 100 μm.
 12. The method accordingto claim 6, wherein the content being between 0.5 and 10 mol%. 13.Polymer solutions containing polymers according to claim 1, dissolved inpolar aprotic solvents.
 14. The method according to claim 1, wherein theheating of the particle fraction to temperatures up to 400° C. 15.Molded article containing at least one polymer according to claim
 1. 16.Fiber containing at least one polymer according to claim
 1. 17. Filmcontaining at least one polymer according to claim
 1. 18. Coatingcontaining at least one polymer according to claim 1.